1. Field of the Invention
The present invention relates to the field of explosives, in particular to igniting devices, and more particularly to igniting devices for metal-sheathed linear explosives and pyrotechnics.
2. Description of the Related Art
Linear explosive and pyrotechnic products, such as Linear Shaped Charge (LSC), Mild Detonating Cord (MDC) and Rapid Deflagrating Cord (RDC) are typically initiated using a separate, distinct, electrically initiated ignition device to provide either a brisant, pyrotechnic or high order shock stimulus for the linear explosive material. Of particular interest are linear shaped charge, mild detonating cord and rapid deflagrating cord devices contained within a metal sheath. Linear shaped charge devices having an explosive wrapped in a continuous metallic sheath are commonly used for severing materials. Sheathed mild detonating cord is used to transfer an explosive stimulus in a contained manner and may be used to instantaneously shear certain structures. These products have potential applications in a wide range of applications, such as automotive and commercial aircraft safety systems, aircrew escape and safety systems, military weapon system ignition, event sequencing and submunition dispensing, launch vehicle event sequencing, and various commercial blasting and oilfield applications.
Generally, in such systems, the linear pyrotechnic or explosive device is provided separately from, and must be mounted and installed with, a separate initiation (ignition) device. However, the use of a separate ignition device increases the cost and complexity of the use of these systems. These devices generally must be installed with an adapter to the linear pyrotechnic device, and the installation of the separate ignition device requires labor, adding to the cost. Moreover, with separate ignition devices, there is often a possibility for a mistake in installation, such as failure to remove the safety cap. For failsafe systems, testing of the installed ignition device may also be difficult.
Moreover, conventional initiators or detonators have some risk of accidental initiation due to electrostatic discharge (ESD) or electromagnetic radiation, which is an important safety and handling issue. In addition, most conventional initiation devices have a lifetime which may be considerably shorter than that of the linear pyrotechnic or explosive, therefore limiting the life of the installed system.
Examples of the conventional art of initiating devices are seen in the following U.S. patents. U.S. Pat. No. 4,070,970, to Scamaton, entitled ELECTRO-EXPLOSIVE IGNITERS, describes an electrically initiated igniter having a layer of pyrotechnic mixture packed between two initiating electrodes. This is a separate device from the actual explosive, and is for non-brisant initiation; a detonator capsule must be attached for brisant ignition.
U.S. Pat. No. 4,312,271, to Day et al., entitled DELAY DETONATION DEVICE, describes a delay detonator device having a bridge wire which ignites a delay charge.
U.S. Pat. No. 4,422,381, to Barrett, entitled IGNITER WITH A STATIC DISCHARGE ELEMENT AND FERRITE SLEEVE, describes an electroexplosive device with a cylindrical electrically conductive metal casing which is open at one end, and which has a bridge element and lead wires.
U.S. Pat. No. 4,976,200, to Benson et al., entitled TUNGSTEN BRIDGE FOR THE LOW ENERGY INITIATION OF EXPLOSIVE AND ENERGETIC MATERIALS, describes a device fabricated on a silicon-on-sapphire substrate.
U.S. Pat. No. 5,036,769, to Schaff et al., entitled PYROFUZE PIN FOR ORDNANCE ACTIVATION, describes a device designed to avoid accidental arming of ordnance, and having a Pyrofuze pin, a connecting ignitor transfer charge, ignitor and electrical terminals in a weatherproof housing.
U.S. Pat. No. 5,225,621, to Kannengiesser et al., entitled PROCESS FOR PRODUCING A JACKETED FUSE AND FUSE PRODUCT, describes a fuse with a jacket produced from a shrinkable hose which is shrink-fitted onto unfinished cord containing an explosive.
U.S. Pat. No. 5,392,713, to Brown et al., entitled SHOCK INSENSITIVE INITIATING DEVICES, describes a device which has a thin elongated metal casing containing a quantity of hydrated metal picrate and an ignition means which may be an electric match.
Based on our reading of the art, then, we have decided that what is needed is an improved system for initiation of linear pyrotechnic devices.
It is therefore an object of the present invention to provide an improved ignition device for metal-sheathed linear explosives and pyrotechnics.
It is a further object of the invention to provide a less complex ignition device.
A still further object of the invention is to provide a linear initiation system which is easier to install.
A yet further object of the invention is to provide a linear initiation system which is less expensive.
Another object of the invention is to provide a linear initiation system which has a longer service life.
Yet another object of the invention is to provide a linear initiation system which is less susceptible to electrostatic discharge and electromagnetic radiation.
Still another object of the invention is to provide a linear initiation system which is more reliable.
These objects are achieved in the linear ignition system of the present invention. One embodiment of the present invention includes two metal-sheathed linear explosives, the ends of which are connected by a non-electrically conducting sleeve leaving a gap between the ends. Bridging this gap is a bridge made from an exothermic metal composition, and electrical contacts are made to each of the metal sheaths of the two linear explosives. Upon application of voltage, current flows through the sheaths, ignites the bridge, when in turn ignites the linear explosive. Here, the term xe2x80x9cexplosivexe2x80x9d is used generally, and covers high explosives which detonate, low explosives which are classed as mild or rapid deflagrating materials, as well as pyrotechnics.
Additional embodiments are presented in which booster increments are included placed against each end of the linear explosive to allow initiation of explosives requiring detonation. Embodiments are described in which an explosive material is included in the gap, and in some embodiments, a hotwire bridge is used instead of the exothermic metal composition.
In another embodiment, the ends of two metal-sheathed linear explosives are connected by a non-conducting sleeve, leaving an unbridged air gap between the ends. Here, application of sufficient voltage across the metal sheaths leads to a spark in the gap, causing ignition. In another embodiment, the gap contains an explosive material. It is also possible to have booster increments on the end of each linear explosive and to provide electrical contacts around the booster increments with the gap formed between the booster increments. In this embodiment, the spark would occur in the gap between the booster increments and ignite the booster increments.
In another embodiment of the invention, a single metal-sheathed linear explosive is covered at one end by an insulating sleeve and a metal end cap over the sleeve, forming a gap between the end of the linear explosive and the inside end of the end cap. A bridge made of an exothermic material extends across the gap within the end cap from the metal sheath to the metal end cap. Electrical contacts are made to the metal end cap and the metal sheath for ignition of the bridge to ignite the linear explosive. Additional embodiments having the end cap are presented in which a booster increments is placed against each the end of the linear explosive, in which an explosive material is included in the gap, or in which a hotwire bridge is used instead of the exothermic metal composition.
Embodiments are also described in which no bridge is present in the gap between the end cap and the end of the linear pyrotechnic, and in which the gap serves as a spark gap. Here, a booster element or an explosive mixture in the gap may also be provided.